1. Field of the Invention
This invention relates to a linear motion rolling guide unit in which a casing-carrying slider is formed so that it can be moved slidingly on a track rail via rolling elements.
2. Description of the Prior Art
In a conventional linear motion rolling guide unit, a slider saddling and moving slidingly on a track rail has a casing, end caps fixed to both ends of the casing, side seals fixed to both end surfaces of the end caps, underseals fixed to a lower surface of the slider, and rolling elements rolling on raceways formed between raceway grooves provided in the track rail and those provided in the casing.
A four-row endless linear motion rolling guide unit is known as a conventional linear motion rolling guide unit described above. The four-row endless linear motion rolling guide unit will now be described with reference to FIGS. 5 and 6. FIG. 5 is a partially cutaway view in perspective of an example of the four-row endless linear motion rolling guide unit, and FIG. 6 a sectional view showing an example of the condition of cylindrical rollers inserted rollably between a track rail and a slider in the four-row endless linear motion rolling guide unit of FIG. 5.
The four-row endless linear motion rolling guide unit has a track rail 1, a slider 7 saddling on the track rail 1 so that the slider can be moved relatively to and slidingly on the track rail 1, and rolling elements 6 interposed rollably between the track rail 1 and slider 7. The track rail 1 is provided in its both lengthwise extending side wall surfaces 2 with grooves 5 constituting raceway surfaces 3. The upper and lower edge portions of the raceway surfaces 3 of the grooves 5 in the track rail 1 from inclined surface portions. In order to have the slider 7 straddle the track rail 1, it has a casing 8 provided with wings 4 defining recesses 9, and end caps 22 fixed to both of the lengthwise end surfaces of the casing 8. In order to seal the clearances between the track rail 1 and end caps 22 during a sliding movement of the slider 7 on the track rail 1, side seals 36 are fixed to the end surfaces of the end caps 22. In order to seal the clearances between the track rail 1 and casing 8 and end caps 22, underseals 26 are fixed to a lower surface of the slider 7 with bolts 35 so that the underseals 26 are also fastened to the casing 8 or end caps 22.
The portions of the recesses 9 in the casing 8 which correspond to the upper and lower raceway surface portions 3 of the track rail 1 are provided with upper and lower raceway surfaces 10. Locking recesses 12 are provided between the upper and lower raceway surfaces 10 of the casing 8. Retainer members 18 having at both of the longitudinal side edge portions thereof locking edges 19 for retaining rolling elements 6 on the casing 8 are engaged with the locking recesses 12 in the casing 8. The retainer members 18 are fixed to the casing 8 by bolts 20 inserted into bolt inserting bores 13 formed in the casing 8, and parts of the retainer members 18 are loosely fitted in the grooves 5 in the track rail 1.
Owing to the above-described construction, the four-row endless linear motion rolling guide unit has load raceways allowing a total of four rows of rolling elements to roll on both side surfaces of the track rail 1, i.e., two rows of rolling elements on each side surface of the track rail 1, and comprising the upper and lower raceway surfaces 3 of the track rail 1 and the upper and lower raceway surfaces 10 of the casing 8. The casing 8 is provided with return passages 14, and the end caps 22 direction conversion passages 21 which allows the load raceways to communicate with return passages 14. Accordingly, the load raceways, direction conversion passages and return passages 14 constitute two endless roller circulating passages. These endless circulating passages are formed so as to cross each other without interfering with each other. When the slider 7 is moved slidingly on the track rail 1, the rolling elements 6 roll circulatingly in the endless circulating passages.
Although examples of rolling elements comprising cylindrical rollers are illustrated in this linear motion rolling guide unit, rolling elements consisting of balls have been developed. In this linear motion rolling guide unit, underseals are attached to the lower surface of the slider for the purpose of effecting the sealing of the contact surfaces of the track rail and casing and end caps. What is disclosed in Japanese Utility Model Laid-Open No. 20923/1994 will now be described as an example of such a linear motion rolling guide unit with reference to FIGS. 7 and 8. FIG. 7 is an exploded view in perspective showing the relation between an end cap and an underseal in the linear motion rolling guide unit, and FIG. 8 a sectional view of an underseal fixing structure in the linear motion rolling guide unit shown in FIG. 7. In FIGS. 7 and 8, the parts the construction and effects of which are identical with those of the above-described conventional linear motion rolling guide unit are designated by the same reference numerals, and the duplication of descriptions thereof is omitted.
In the linear motion rolling guide unit shown in FIGS. 7 and 8, an end cap 22 is provided with a projection 23 extending from a lower surface thereof in the longitudinal direction, and this projection 23 has longitudinally extending locking portions 24. Locking claws 29 are formed by longitudinal edge portions of a locking bore 28 formed so as to extend longitudinally in a core metal member 27 of the underseal 26, and the projection 23 is engaged with the locking claws 29 by elastically deforming the former, whereby the underseal 26 is secured to the end cap 22.
In the linear motion rolling guide units shown in FIGS. 5-8, each underseal 26 is fixed to the lower surface of the end cap 22 by a bolt 35 or a projection 23. Regardless of the method of fixing the underseal 26 to the end cap 22, the underseal 26 is fixed to the lower surface of the casing 8 or end cap 22 so that a lip portion 31 or a contacting portion 32 of an elastic member 30 of the underseal 26 closely engages the track rail 1, end cap 22 and casing 8. The whole or a part of the underseal 26 is positioned below the lower surface of the end cap 22.
In the linear motion rolling guide unit shown in FIGS. 7 and 8, the end cap 22 is provided with a projection 23 extending longitudinally from the lower surface thereof, and the locking claws 29 formed at the longitudinal edge portions of the locking bore 28 provided so as to extend longitudinally in the core metal member 27 of the underseal 26 are engaged with the locking portions 24 provided on the projection 23 as mentioned above. Therefore, in this linear motion rolling guide unit, the projection 23 is fitted in the locking bore 28 by elastically deforming the former, and the locking portions 24 of the projection 23 are engaged with the locking claws 29 of the locking bore 28, whereby the underseal 26 is attached to the end cap 22. Consequently, the projection 23 requires an elasticity for fitting itself in the locking bore 28, and a rigidity for locking the locking claws 29 by the locking portions 24, so that the manufacturing of these parts becomes complicated and very expensive.
The projection 23 formed on the lower surface of the end cap 22 of this linear motion rolling guide unit is elastically deformed when the underseal 26 is fixed or removed, so that it is liable to be broken. Moreover, since the projection 23 is formed integrally with the end cap 22, it is necessary that the end cap 22 as a whole be replaced even when the projection 23 only is broken.
FIG. 9 is a schematic illustration showing a linear motion rolling guide unit similar to that of FIG. 6. As shown in FIG. 9, a height H1 measured from a lower surface of a slider 7 to that of a track rail 1 with the slider 7 straddling the track rail 1 in a conventional linear motion rolling guide unit, i.e. a satisfactory distance between a base 37 on which the track rail 1 is fixed and the lower surface of the slider 7 cannot be secured. Therefore, limitations are placed on the designing of the construction of the slider 7, i.e., the degree of freedom of designing the slider 7 is restricted.